1. Field of the Invention
Embodiments of the invention generally relate to an electromagnetically levitated substrate support.
2. Background of the Related Art
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip design continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. One fabrication process frequently used is ion implantation.
Ion implantation is particularly important in forming transistor structures on semiconductors and may be used many times during chip fabrication. During ion implantation, silicon substrates are bombarded by a beam of electrically charged ions, commonly called dopants. Implantation changes the properties of the material in which the dopants are implanted to achieve a particular level of electrical performance. Dopant concentration is determined by controlling the number of ions in a beam of energy projected on the substrate and the number of times the substrate passes through the beam. The energy level of the beam typically determines the depth at which the dopants are placed. These dopants are accelerated to an energy level that will permit the dopants to penetrate or implant into the film at a desired depth.
During ion implantation, the implanted film often develops a high level of internal stress. In order to relieve the stress and further control the resulting properties of the implanted film, the film is typically subjected to a thermal process, such as annealing. Post-ion implantation annealing is typically performed in a rapid thermal processing (RTP) chamber that subjects the substrate to a very brief, yet highly controlled thermal cycle that can heat the substrate from room temperature to over 1000xc2x0 C. in under 10 seconds. RTP relieves the stress induced during implantation and can be used to further modify film properties such as changing the electrical characteristics of the film.
Generally, an RTP chamber includes a radiant heat source or lamp, a chamber body and a substrate support ring. The lamp is typically mounted to a top surface of the chamber body so that the radiant energy generated by the lamp impinges upon the substrate supported by the support ring within the chamber body. A quartz window is typically disposed in the top surface of the chamber body to facilitate the transfer of energy between the lamp and the substrate. The support ring is typically comprised of silicon carbide and extends from a bottom of the chamber body to support the substrate by its outer edge. An external motor is used to rotate the substrate and the support ring to compensate for variations in the radiant energy generated by the lamp impinging across the substrate surface that could heat the substrate non-uniformly. Typically, the RTP process is performed at a reduced pressure to minimize potential particle and chemical contamination of the substrate.
U.S. Pat. No. 5,818,137, issued Oct. 6, 1998 to Nichols et al., describes an RTP chamber that is adapted to reduce particle contamination. Nichols, et al. describes a rotary motor and magnetic bearing that levitates a substrate supported within an RTP chamber, thus eliminating a bearing that conventionally supports the substrate support, thus removing a potential source of substrate contamination and particle generation. Generally, a stator assembly is coupled to the exterior of the RTP chamber and is magnetically coupled to a rotor. The rotor is coupled to the substrate support. When energized, the stator assembly levitates and passively centers the rotor along a vertical axis.
However, the Nichols et al. device requires precise control of stator energization in order to levitate the rotor and substrate support. A controller is coupled to a plurality of sensors to provide rotor positional information. The information is utilized by the controller to energize various control coils wound on each stator pole in response to the sensed physical position of the rotor. The chamber hardware and software required to provide such precise control is costly and subject to error which may result in damage to the substrate or poor processing results.
Moreover, mounting of the stator to the chamber body requires high precision to ensure the parallelism between the heating lamp and the substrate supported on the ring in order to minimize deviations in radial energy transferred across the diameter of the substrate. The careful fabrication and close tolerances needed to achieve good parallelism results in high system costs. Furthermore, it is desirable to eliminate other moving parts, such as lift pins, to further reduce particulate generation and system complexity.
Therefore, is a need for an improved substrate support.
An apparatus for supporting a substrate and a method for positioning a substrate are generally provided. In one embodiment, an apparatus for supporting a substrate includes a substrate support, a stator circumscribing the substrate support, and an actuator. The actuator is coupled to the stator and adapted to control the elevation of the stator and/or adjust an angular orientation of the stator relative to its central axis. As the substrate support is magnetically coupled to the stator, particle generating contact between the substrate support and other components is avoided while the elevation and angular orientation of a substrate disposed on the substrate support may be advantageously controlled.
In another embodiment, a processing chamber is provided. The processing chamber generally includes a chamber body having a substrate support disposed therein and a stator circumscribing the chamber body. The stator is magnetically coupled to the substrate support. An actuator is coupled to the stator and adapted to control the elevation and/or angular orientation of the stator.
In another embodiment, a method for positioning a substrate is provided. The method includes positioning a substrate supported on a robot blade above a magnetically levitating substrate support and elevating a stator magnetically coupled to the substrate support to lift the substrate from the blade.
In another embodiment, a method for positioning a substrate includes providing a substrate seated on a substrate support, and moving a stator magnetically coupled to the substrate support, thus controlling the elevation and/or orientation of the substrate support.
In another embodiment, a method for supporting a substrate includes providing a substrate support disposed in a process chamber, magnetically levitating the substrate support, and moving a stator along a central axis of the process chamber to control the elevation and/or orientation of the substrate support magnetically coupled thereto.